The objective of this proposal is the further elucidation of the mechanisms of the vertebrate olfactory system, with the particular focus on the mechanism of processing of olfactory stimuli in the OE and the OB. A longer term aim is to reveal the processes behind the formation, storage, and retrieval of information related to olfactory stimuli. Several points are addressed in this proposal: to show directly how and which sensory neurons in the OE detect different odors, to establish the role of the olfactory bulb with specific attention to the mechanism of discrimination between odors, and to identify the downstream elements of the brain involved in storing memories of odors. Confocal microscopy will be used to accomplish these aims using the almost transparent larval zebrafish as the model system. A calcium probe will be incorporated into the neurons of zebrafish by a variety of methods and the activity of neurons monitored by fluctuations of intracellular calcium levels, as indicated by changes in probe fluorescence monitored by confocal microscopy. Using this experimental paradigm it is possible to observe ensembles of neurons simultaneously in live fish in real-time. It is this crucial ability which allows for the first time a direct attack on the problem of coding and storage of sensory information in a vertebrate.